The present invention relates generally to methods and systems for production of hydrocarbons from various subsurface subterranean formations. The present invention, downhole steam injection, is a novel approach to a very successful application of surface steam injection into heavy oil reservoirs that began in the late 1950's. Today, steam injection is also used in light oil formations to increase recovery of residual oil after depletion of reservoir pressure. Pressurized steam can add new pressure to the light oil subterranean deposit while the steam melts the oil off the rock the steam condenses to water and the water will act as a drive mechanism to push the oil through the reservoir to the production wells.